Superconducting magnetic bearing

ABSTRACT

A superconductive magnetic bearing  22  comprises a stationary bearing portion  23  having an annular superconductor unit  26  provided on a fixed portion  20 , and a rotatable bearing portion  24  having annular permanent magnet units  28, 29  provided on a rotary portion  21  so as to be opposed to the superconductor unit  26 . The rotary portion  21  is contactlessly supported relative to the fixed portion  20  by the pinning effect of a superconductor constituting the superconductor unit  26 . The permanent magnet units  28, 29  each comprise a plurality of permanent magnet members arranged in superposed layers with an insulating layer provided between each adjacent pair of magnet members.

TECHNICAL FIELD

The present invention relates to superconductive magnetic bearingswherein a rotatable portion is contactlessly supported relative to astationary portion utilizing the pinning effect of a superconductor ofthe second kind.

BACKGROUND ART

Superconductive magnetic bearings of the type mentioned and alreadyknown include those comprising a stationary bearing portion having anannular superconductor unit provided on a stationary portion, and arotatable bearing portion having an annular permanent magnet unitprovided on a rotatable portion so as to be opposed to thesuperconductor unit. Such superconductive magnetic bearings furtherinclude superconductive magnetic bearings of the radial type wherein thetwo bearing portions are opposed radially of the bearing, and those ofthe axial type wherein the two bearing portions are opposed axially ofthe bearing.

FIG. 1 shows an example of conventional superconductive magnetic bearingof the radial type.

With reference to FIG. 1, indicated at 1 is a stationary portion in theform of a shaft, and at 2 a rotatable portion in the form of a hollowcylinder and rotatable around the stationary portion 1. The stationaryportion 1 is provided with a stationary bearing portion 3, and therotatable portion 2 with a rotatable bearing portion 4.

The stationary bearing portion 3 has a superconductor unit 5 in the formof a hollow cylinder. As shown in FIG. 2, the superconductor unit 5comprises a plurality of superconductor bulks 6 in the form ofcircumferentially divided segments of a hollow cylinder. Each of thesuperconductor bulks 6 comprises a superconductor of the second kindhaving fine normally conductive particles uniformly incorporatedtherewith. The superconductor bulks 6 are cooled as with liquidnitrogen.

The rotatable bearing portion 4 has two hollow cylindrical permanentmagnet units 7, 8 arranged side by side axially of the bearing, andthree annular yokes 9 of magnetic material arranged between the adjacentend faces of the two magnet units 7, 8 and over the other end facesthereof. Although not shown in detail, each permanent magnet units 7 (8)comprises a plurality of permanent magnet bulks 10 (11) in the form ofcircumferentially divided segments of a hollow cylinder. The permanentmagnet units 7, 8 each have magnetic poles at axial (upward anddownward) opposite ends thereof. The adjacent ends of the two permanentmagnet units 7, 8 have the same polarity. In this case, the upper unit 7has an N pole at its upper end and an S pole at its lower end, and thelower unit 8 has an S pole at its upper end and an N pole at its lowerend.

The upper permanent magnet unit 7 sets up a magnetic field indicated byan arrow A in FIG. 1 between the magnet unit 7 and the upper portion ofthe superconductor unit 5. Similarly, the lower permanent magnet unit 8sets up a magnetic field indicated by an arrow B in FIG. 1 between themagnet unit 8 and the lower portion of the superconductor unit 5. Whenthe superconductor unit 5 is brought into a superconducting state bycooling, the magnetic fields penetrating into the unit 5 are captured at(pinned to) normally conductive portions (pinning points) of the normalconductor particles in the interior of the unit 5, and the rotatablebearing portion 4 is supported by this pinning effect with respect tothe axial and radial directions relative to the stationary bearingportion 3.

In the permanent magnet units 7, 8 of the superconductive magneticbearing described above, the permanent magnet bulks 10, 11 arecircumferentially uniform in magnetic field, but the boundaries betweenadjacent magnet bulks 10, 11 are not uniform in magnetic field. Theyokes 9 are used to diminish such circumferential unevenness of magneticfields, and the presence of the yokes 9 enables the permanent magnetunits 7, 8 to set up substantially uniform magnetic fields. Accordingly,the magnetic fields remain unaltered to produce no resistance torotation despite the rotation of the magnet units 7, 8 with therotatable portion 2. The circumferentially uniform magnetic fields arecaptured at the pinning points of the superconductor unit 5 as describedabove.

On the other hand, the superconductor unit 5 has the problem that sincethe unit 5 is divided into a plurality of superconductor bulks 6 asarranged circumferentially thereof, the magnetic fields set up by theunit 5 are uneven with respect to the circumferential direction.

A description will be given of the superconductor bulks 6 wherein themagnetic fields provided by the permanent magnet units 7, 8 arecaptured. As shown in FIG. 2, the magnetic field is captured at a largenumber of pinning points 12 in each superconductor bulk 6, and ashielding current indicated by an arrow C flows around the point 12. Themagnetic field set up by this shielding current becomes a magnetic fieldcaptured by the bulk 6. Inside the bulk 6, the pinning points 12 areuniformly distributed with respect to the circumferential direction, sothat the magnetic fields captured are uniform. At the portion ofboundary between adjacent superconductor bulks 6, the distribution ofpinning points 12 is uneven, and the magnetic fields are also uneven.When this is observed macroscopically, the shielding currents around thepinning points 12 which are uniformly distributed offset one another,whereas at the boundary between superconductor bulks 6, the shieldingcurrents around the outermost pinning points 12 are not offset, with theresult that when the bulk 6 is observed in its entirety, a shieldingcurrent flows as indicated in a broken line D in FIG. 2. Since suchshielding current flows through every bulk 6, the superconductor unit 5becomes uneven in magnetic field with respect to the circumferentialdirection. If the magnetic fields set up by the unit 5 becomecircumferentially uneven, the permanent magnet units 7, 8 are subjectedto varying magnetic fields when rotating with the rotatable portion 2,producing eddy currents in the units 7, 8 and giving rise to a rotationloss,

Eddy currents also occur in the yokes 9 owing to the circumferentialunevenness of magnetic fields in the superconductor unit 5.

An object of the present invention is to overcome the above problem andto provide a superconductive magnetic bearing which is diminished in theeddy currents occurring in the permanent magnet units and in the yokesdue to the unevenness of magnetic fields set up by the superconductorunit to ensure a reduced rotation loss.

DISCLOSURE OF THE INVENTION

The present invention provides a superconductive magnetic bearingcomprising a stationary bearing portion having an annular superconductorunit provided on a fixed portion, and a rotatable bearing portion havingan annular permanent magnet unit provided on a rotary portion so as tobe opposed to the superconductor unit, the rotary portion beingcontactlessly supported relative to the fixed portion by the pinningeffect of a superconductor constituting the superconductor unit, thesuperconductive magnetic bearing being characterized in that thepermanent magnet unit comprises a plurality of permanent magnet membersarranged in superposed layers with an insulating layer provided betweeneach adjacent pair of magnet members.

The permanent magnet members are arranged in superposed layers in atleast one of the axial direction and the radial direction.

For example, permanent magnet members each in the form of a disk havinga hole are arranged in superposed layers axially of the bearing. Forexample, permanent magnet members each in the form of a thin hollowcylinder are arranged in superposed layers radially of the bearing.Further for example, a plurality of annular permanent magnet memberseach having a square or rectangular cross section are arranged insuperposed layers both axially and radially of the bearing.

Each permanent magnet member may be an integral piece extending over theentire circumferential direction or may comprise a plurality ofcircumferentially divided circular-arc segments. Thus, the permanentmagnet members are arranged in superposed layers in at least one of theaxial direction, radial direction and circumferential direction.

In the case where the superconductive magnetic bearing is of the radialtype wherein the stationary bearing portion and the rotatable bearingportion are opposed radially of the bearing, for example, a plurality ofpermanent magnet members each in the form of a disk having a hole arearranged in superposed layers axially of the bearing. Alternatively, aplurality of annular permanent magnet members are arranged in superposedlayers both axially and radially of the bearing.

In the case where the superconductive magnetic bearing is of the axialtype wherein the stationary bearing portion and the rotatable bearingportion are opposed axially of the bearing, for example, a plurality ofpermanent magnet members each in the form of a thin hollow cylinder arearranged in superposed layers radially of the bearing. Alternatively, aplurality of annular permanent magnet members are arranged in superposedlayers both axially and radially of the bearing.

With the superconductive magnetic bearing of the invention, thepermanent magnet unit comprises a plurality of permanent magnet membersarranged in superposed layers with an insulating layer provided betweeneach adjacent pair of magnet members, so that even when the permanentmagnet unit is subjected to varying magnetic fields, the eddy currentsto be produced in the magnet units diminish to ensure a reduced rotationloss.

Accordingly, the superconductive magnetic bearing of the invention canbe diminished in the eddy currents to be produced in the magnet unit toreduce the rotation loss.

Preferably the superconductor unit continuously extends over the entirecircumferential direction, whereas for the convenience of fabrication,the superconductor unit usually comprises a plurality ofcircumferentially divided superconductor bulks.

In the case where the superconductor unit comprises a plurality ofcircumferentially divided superconductor bulks, the magnetic fields tobe set up by the superconductor units become uneven with respect to thecircumferential direction, with the result that the magnetic unit issubjected to varying magnetic fields when rotating with the rotaryportion. With the superconductive magnetic bearing of the presentinvention, however, the permanent magnet unit comprises a plurality ofpermanent magnet members arranged in superposed layers with aninsulating layer provided between each adjacent pair of magnet members.This construction diminishes the eddy currents to be produced in themagnet unit and also reduces the rotation loss due to the eddy currents.

Thus, the construction described above diminishes the eddy currents tobe produced in the permanent magnet unit due to the unevenness of themagnetic fields to be set up by the superconductor unit to reduce therotation loss that would otherwise result.

For example, the rotatable bearing portion comprises the annularpermanent magnet unit and an annular yoke adjacent to the permanentmagnet unit and opposed to the superconductor unit, the yoke comprisinga plurality of yoke members made of a magnetic material and arranged insuperposed layers with an insulating layer interposed between eachadjacent pair of yoke members.

For example, a silicon steel sheet is used as the magnetic material forthe yoke members.

In the case of a superconductive magnetic bearing of the radial type,for example, yoke members each in the form of a disk having a hole arearranged in superposed layers axially of the bearing. In the case of asuperconductive magnetic bearing of the axial type, for example, yokemembers each in the form of a thin hollow cylinder are arranged insuperposed layers radially of the bearing.

The rotatable bearing portion has at least one permanent magnet unit.

In the case where one permanent magnet unit is provided, the yoke isprovided preferably at each of two locations on opposite sides of themagnet unit.

Preferably, the rotatable bearing portion has a plurality of permanentmagnet units. More preferably, two permanent magnet units are provided.In the case where the rotatable bearing unit has two magnet units, theyoke is disposed preferably at three locations, i.e., between the twomagnet units and on opposite sides of the magnet unit arrangement.

In the case of the superconductive magnetic bearing of the radial type,for example, two permanent magnet units are arranged axially of thebearing, and the yoke is positioned at three locations, i.e., betweenthese magnet units and on axial opposite sides of the magnet unitarrangement.

In the case of the superconductive magnetic bearing of the axial type,for example, two permanent magnet units are arranged radially of thebearing, and the yoke is positioned at three locations, i.e., betweenthese magnet units and on radial opposite sides of the magnet unitarrangement.

The yoke comprises yoke members as arranged in superposed layers in atleast one of the axial direction and radial direction, preferably inmany directions if structurally possible.

When the yokes are subjected to varying magnetic fields while rotatingwith the rotary portion, eddy currents are produced also on the yokes,whereas if the yokes each comprise yoke members of magnetic material asarranged in superposed layers with an insulating layer provided betweeneach adjacent pair of yoke members, the eddy currents to be produced onthe yokes diminish to reduce the rotation loss to be otherwise producedby the eddy currents.

Thus, the construction described above diminishes the eddy currents tobe produced in the permanent magnet units and in the yokes due to theunevenness of the magnetic fields to be set up by the superconductorunit to reduce the rotation loss.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view in vertical section schematically showing an example ofconventional superconductive magnetic bearing of the radial type.

FIG. 2 is a perspective view showing the portion of a superconductorunit in FIG. 1.

FIG. 3 is a view in vertical section of a superconductive magneticbearing of the radial type to show a first embodiment of the invention.

FIG. 4 is a fragmentary perspective view partly broken away and showinga rotatable bearing portion of FIG. 1.

FIG. 5 is a fragmentary exploded perspective view partly broken away andshowing the rotatable bearing portion of FIG. 1.

FIG. 6 is a fragmentary perspective view partly broken away and showinga modification of a permanent magnet unit included in the firstembodiment.

FIG. 7 is a view in vertical section of a superconductive magneticbearing of the axial type to show a second embodiment of the invention.

FIG. 8 is a fragmentary perspective view partly broken away and showinga rotatable bearing portion of FIG. 7.

FIG. 9 is a fragmentary exploded perspective view partly broken away andshowing the rotatable bearing portion of FIG. 7.

BEST MODE OF CARRYING OUT THE INVENTION

Two embodiments of the invention will be described below with referenceto FIGS. 3 to 9.

FIGS. 3 to 5 show a first embodiment.

FIG. 3 shows a superconductive magnetic bearing 22 of the radial typewherein a rotatable body 21 which is a portion rotatable relative to astationary portion 20 is contactlessly supported. The superconductivemagnetic bearing 22 comprises a stationary bearing portion 23 providedon the stationary portion 20, and a rotatable bearing portion 24provided on the rotatable body 21.

The stationary portion 20 has an annular cooling tank 25 centered abouta vertical axis of the stationary portion 20. The stationary bearingportion 23 is provided at an outer peripheral portion of the interior ofthe tank 25.

The stationary bearing portion 23 comprises a superconductor unit 26 inthe form of a hollow cylinder and fixed concentrically to the outerperipheral portion of the interior of the tank 25. Although not shown indetail, the superconductor unit 26 comprises a plurality ofcircumferentially divided superconductive bulks 27. Each ofsuperconductor bulks 27 comprises a superconductor of the second kindhaving fine normally conductive particles uniformly incorporatedtherein. According to the present embodiment, the superconductor bulks27 comprise yttrium-base superconductor, i.e., yttrium 123(YBa₂Cu₃O_(7-x)), having uniformly incorporated therein fine particlesof a yttrium-base normal conductor, i.e., yttrium 211 (Y₂BaCu).

The tank 25 is connected to an unillustrated suitable cooling device bya cooling fluid supply pipe 46 and a cooling fluid discharge pipe 47. Acooling fluid comprising, for example, liquid nitrogen is circulatedthrough the tank 25 by the cooling device, and the superconductor unit26 is cooled by the cooling fluid filling the tank 25.

The rotatable body 21 comprises a vertical shaft portion 21 a disposedabove the stationary portion 20 concentrically therewith, a disk portion21 b fixed to the lower end of the shaft portion 21 a concentricallytherewith, and a hollow cylindrical support portion 21 c fixed to thelower side of the disk portion 21 b concentrically therewith. Therotatable bearing portion 24 is provided on the inner peripheral portionof the cylindrical portion 21 c.

The rotatable bearing portion 24 comprises two hollow cylindricalpermanent magnet units 28, 29 and three hollow cylindrical yokes 30which are opposed to and positioned radially outwardly of thesuperconductor unit 26, and spaced therefrom by a small clearance. Thetwo magnet units 28, 29 are arranged side by side axially of the unit 26(in the upward or downward direction). The yokes 30 are arrangedadjacent to the opposed lower and upper end faces of the upper and lowerpermanent magnet units 28, 29, to the upper end face of the upper magnetunit 28 and to the lower end face of the lower magnet unit 29. Each ofthe magnet units 28, 29 have magnetic poles at the upper and lower endsthereof, and the adjacent ends of the two magnet units 28, 29 have thesame polarity. According to the present embodiment, the upper magnetunit 28 has an N pole at its upper end and an S pole at its lower end,and the lower magnet unit 29 has an S pole at its upper end and an Npole at its lower end.

The rotatable bearing portion 24 is shown in detail in FIGS. 4 and 5.FIG. 4 is a fragmentary perspective view partly broken away and showingthe rotatable bearing portion 24. FIG. 5 is a fragmentary perspectiveview partly broken away and showing the bearing portion 24 asdisassembled.

Each of the yokes 30 comprises a plurality of yoke members 32 made of amagnetic material, each in the form of a disk having a hole and arrangedin superposed layers axially of the bearing with an insulating layer 31provided between each adjacent pair of yoke members 32. Each of the yokemembers 32 is an integral piece made, for example, of a silicon steelsheet and extending over the entire circumference. The yoke member 32 isprovided with an insulating film formed over each of its upper and lowersurfaces to provide the insulating layer 31.

Each permanent magnet unit 28 (29) comprises a plurality of permanentmagnet members 35 (36) each in the form of a disk having a hole andarranged in superposed layers axially thereof with an insulating layer33 (34) provided between each adjacent pair of magnet members 35 (36).Each of the magnet members 35 (36) is provided with an insulating filmformed over each of its upper and lower surfaces to provide theinsulating layer 33 (34).

Each of the permanent magnet members 35, 36 may be an integral pieceextending over the entire circumferential direction or may comprise aplurality of divided circular-arc segments which are arranged in thecircumferential direction. According to the present embodiment, thepermanent magnet member 35 (36) comprises a plurality ofcircumferentially divided circular-arc segments 35 a (36 a).

With reference to FIG. 5, the upper permanent magnet unit 28 comprises aplurality of circumferentially divided segmental cylindrical blocks 37.Each of the blocks 37 comprises a plurality of circular-arc segments 35a arranged in superposed layers in the axial direction. Eachcircular-arc segment 35 a is, for example, about 0.5 mm in thickness inthe upward or downward direction. The circular-arc segment 35 a has aninsulating film formed over each of its upper and lower surfaces toprovide the insulating layer 33. The circular-arc segment 35 a hasmagnetic poles at the respective upper and lower surfaces thereof, i.e.,an N pole at the upper surface and an S pole at the lower surface. Whensuch circular-arc segments 35 a are arranged in superposed layers, theblock 37 has in its entirety an N pole at its upper end and an S pole atits lower end. The permanent magnet unit 28 is provided by arranging aplurality of blocks 37 in the circumferential direction between theupper and lower yokes 30.

The lower permanent magnet unit 29 also comprises a plurality ofsegmental cylindrical blocks 38 each comprising a plurality ofcircular-arc segments 36 a arranged in superposed layers in the axialdirection. In the case of the lower magnet unit 29, the circular-arcsegment 36 a has an S pole at the upper surface and an N pole at thelower surface, and the block 38 has in its entirety an S pole at itsupper end and an N pole at its lower end. With the exception of thesefeatures, the lower magnet unit 29 is the same as the upper magnet unit28.

With the superconductive magnetic bearing 22 described above, themagnetic fields set up by the permanent magnet units 28, 29 penetrateinto the superconductor unit 26 when the unit is in the normalconducting state as in the environment of room temperature. When thesuperconductor unit 26 in this state is brought into a superconductingstate by cooling, the magnetic fields penetrating into superconductorunit 26 are captured at the pinning points in the interior of the unit26, and the rotatable bearing portion 24 is contactlessly supportedrelative to the stationary bearing portion 23 with respect to the axialand radial directions by virtue of this pinning effect.

Although the permanent magnet units 28, 29 are circumferentially dividedinto blocks 37, 38, the yokes 30 provided render the magnetic fields ofthe units 28, 29 substantially uniform with respect to thecircumferential direction. Accordingly, even if the magnet units 28, 29rotate with the rotatable body 21, the magnetic fields remain unalteredto produce no resistance to rotation. The magnetic fields which arecircumferentially uniform are captured at the pinning points of thesuperconductor unit 26.

Since the superconductor unit 26 is circumferentially divided into aplurality of superconductor bulks 27, the magnetic fields set up by theunit 26 become circumferentially uneven as previously described, andwhen the rotatable bearing portion 24 rotates with the rotatable body21, the permanent magnet units 28, 29 and the yokes 30 are subjected tochanges in magnetic fields. However, because the permanent magnet units28, 29 comprise permanent magnet members 35, 36 arranged in superposedlayers along with intervening insulating layers 33, 34 and furtherbecause the yokes 30 also comprise yoke members 32 which are arranged insuperposed layers along with insulating layers 31, the eddy currents tobe produced in the magnet units 28, 29 and yokes 30 diminish to reducethe resulting rotational loss.

FIG. 6 shows a modification of the permanent magnet unit of the firstembodiment.

The permanent magnet unit 40 shown comprises a plurality of annularpermanent magnet members 41 having a square or rectangular cross sectionand arranged in superposed layers in both the axial and radialdirections with an insulating layer 42 interposed between each adjacentpair of magnet members.

Each permanent magnet member 41 in this case may be an integral pieceextending over the entire circumferential direction or may comprise aplurality of circumferentially divided circular-arc segments.

FIGS. 7 to 9 show a second embodiment.

FIG. 7 shows a superconductive magnetic bearing 52 of the axial typewherein a rotatable body 51 which is a portion rotatable relative to astationary portion 50 is contactlessly supported. The superconductivemagnetic bearing 52 comprises a stationary bearing portion 53 providedon the stationary portion 50, and a rotatable bearing portion 54provided on the rotatable body 51.

The stationary portion 50 has a flat annular cooling tank 55 centeredabout a vertical axis of the stationary portion 50. The stationarybearing portion 53 is provided at an upper end portion of the interiorof the tank 55.

The stationary bearing portion 53 comprises a superconductor unit 56 inthe form of a relatively thick disk having a hole and fixed to the upperend portion within the tank 55 concentrically therewith. Although notshown in detail, the superconductor unit 56 comprises a plurality ofcircumferentially divided superconductor bulks 57. As in the case of thefirst embodiment, the superconductor bulks 57 comprise a superconductorof the second kind.

The tank 55 is connected to an unillustrated suitable cooling device bya cooling fluid supply pipe 48 and a cooling fluid discharge pipe 49 forcooling the superconductor unit 56 in the same manner as in the firstembodiment.

The rotatable body 51 comprises a vertical shaft portion 51 a disposedabove the stationary portion 50 concentrically therewith, and a supportdisk portion 51 b fixed to the lower end of the shaft portion 51 aconcentrically therewith. The rotatable bearing portion 54 is providedaround the disk portion 51 b.

The rotatable bearing portion 54 comprises two permanent magnet units58, 59 and three yokes 60 which are arranged as opposed to thesuperconductor unit 56 on the axial upper side thereof and spaced fromthe unit 56 by a small clearance. The two magnet units 58, 59 arearranged radially of the rotatable body 51 concentrically therewith. Theyokes 60 are arranged adjacent to the opposed outer and innerperipheries of the respective inner and outer magnet units 58, 59, tothe inner periphery of the inner magnet unit 58 and to the outerperiphery of the outer magnet unit 59. The magnet units 58, 59 havemagnetic poles on the inner and outer peripheral surfaces thereof, andthe adjacent peripheral surfaces of the two unit 58, 59 have the samepolarity. With the present embodiment, the inner magnet unit 58 has an Npole on the inner peripheral surface thereof and an S pole on the outerperipheral surface thereof, and the outer magnet unit 59 has an S poleon the inner peripheral surface and an N pole on the outer peripheralsurface.

The rotatable bearing portion 54 is shown in detail in FIGS. 8 and 9.FIG. 8 is a fragmentary perspective view partly broken away and showingthe rotatable bearing portion 54, and FIG. 9 is a fragmentaryperspective view partly broken away and showing the rotatable bearingportion 54 as disassembled.

Each of the yokes 60 comprises a plurality of yoke members 62 made of amagnetic material, each in the form of a hollow cylinder and arranged insuperposed layers radially thereof with an insulating layer 61 providedbetween each adjacent pair of yoke members 62. Each of the yoke members62 is an integral piece made, for example, of a silicon steel sheet andextending over the entire circumference. The yoke member 62 is providedwith an insulating film formed over each of its inner and outer surfacesto provide the insulating layer 61.

Each permanent magnet unit 58 (59) comprises a plurality of permanentmagnet members 65 (66) each in the form of a hollow cylinder andarranged in superposed layers radially thereof with an insulating layer63 (64) provided between each adjacent pair of magnet members 65 (66).Each of the magnet members 65 (66) is provided with an insulating filmformed over each of its inner and outer surfaces to provide theinsulating layer 63 (64).

Each of the permanent magnet members 65, 66 may be an integral pieceextending over the entire circumferential direction or may comprise aplurality of divided circular-arc segments which are arranged in thecircumferential direction. According to the present embodiment, thepermanent magnet member 65 (66) comprises a plurality ofcircumferentially divided circular-arc segments 65 a (66 a).

With reference to FIG. 9, the inner permanent magnet unit 58 comprises aplurality of circumferentially divided segmental cylindrical blocks 67.Each of the blocks 67 comprises a plurality of circular-arc segments 65a arranged in superposed layers in the radial direction. Eachcircular-arc segment 65 a is, for example, about 0.5 mm in thickness inthe inward or outward direction. The circular-arc segment 65 a has aninsulating film formed over each of its inner and outer surfaces toprovide the insulating layer 63. The circular-arc segment 65 a hasmagnetic poles on the respective inner and outer surfaces thereof, i.e.,an N pole on the inner surface and an S pole at the outer surface. Whensuch circular-arc segments 65 a are arranged in superposed layers, theblock 67 has in its entirety an N pole at its inner surface and an Spole at its outer surface. The permanent magnet unit 58 is provided byarranging a plurality of blocks 67 in the circumferential directionbetween the inner and outer yokes 60.

The outer permanent magnet unit 59 also comprises a plurality ofsegmental cylindrical blocks 68 each comprising a plurality ofcircular-arc segments 66 a arranged in superposed layers in the radialdirection. In the case of the outer magnet unit 59, the circular-arcsegment 66 a has an S pole at the inner surface and an N pole at theouter surface, and the block 68 has in its entirety an S pole at itsinner end and an N pole at its outer end. With the exception of thesefeatures, the outer magnet unit 59 is the same as the inner magnet unit58.

A plurality of annular reinforcing members 69 are provided around therotatable bearing portion 54 concentrically therewith for preventing theexpansion of the yoke members 62 and the permanent magnet members 65, 66due to the centrifugal force produced by high-speed rotation and theresulting break of such members 62, 65, 66. The reinforcing members 69are made, for example, from CFRP (carbon fiber reinforced plastics).

With the superconductive magnetic bearing 52 described above, themagnetic fields set up by the permanent magnet units 58, 59 penetrateinto the superconductor unit 56 when the unit 56 is in the normalconducting state as in the environment of room temperature. When thesuperconductor unit 56 in this state is brought into a superconductingstate by cooling, the magnetic fields penetrating into superconductorunit 56 are captured at the pinning points in the interior of the unit56, and the rotatable bearing portion 54 is contactlessly supportedrelative to the stationary bearing portion 53 with respect to the axialand radial directions by virtue of this pinning effect.

Although the permanent magnet units 58, 59 are circumferentially dividedinto blocks 67, 68, the yokes 60 provided render the magnetic fields ofthe units 58, 59 substantially uniform with respect to thecircumferential direction. Accordingly, even if the magnet units 58, 59rotate with the rotatable body 51, the magnetic fields remain unalteredto produce no resistance to rotation. The magnetic fields which arecircumferentially uniform are captured at the pinning points of thesuperconductor unit 56.

Since the superconductor unit 56 is circumferentially divided into aplurality of superconductor bulks 57, the magnetic fields set up by theunit 56 become circumferentially uneven as previously described, andwhen the rotatable bearing portion 54 rotates with the rotatable body51, the permanent magnet units 58, 59 and the yokes 60 are subjected tochanges in magnetic fields. However, because the permanent magnet units58, 59 comprise permanent magnet members 65, 66 arranged in superposedlayers along with intervening insulating layers 63, 64 and furtherbecause the yokes 60 also comprise yoke members 62 which are arranged insuperposed layers along with insulating layers 61, the eddy currents tobe produced in the magnet units 58, 59 and yokes 60 diminish to reducethe resulting rotation loss.

The permanent magnet unit 58, 59 of the second embodiment may comprise aplurality of annular permanent magnet members having a square orrectangular cross section and arranged in superposed layers in both theaxial and radial directions with an insulating layer interposed betweeneach adjacent pair of magnet members. Each permanent magnet member inthis case may be an integral piece extending over the entirecircumferential direction or may comprise a plurality ofcircumferentially divided circular-arc segments.

INDUSTRIAL APPLICABILITY

As described above, the invention provides a useful superconductivemagnetic bearing for contactlessly supporting a rotatable portionrelative to a stationary portion utilizing the pinning effect of asuperconductor of the second kind. Eddy currents are diminished whichare produced in permanent magnet units and yokes due to uneven magneticfields to be set up by a superconductor unit to reduce the rotationloss.

1. A superconductive magnetic bearing comprising a stationary bearingportion having an annular superconductor unit provided on a fixedportion, and a rotatable bearing portion having an annular permanentmagnet unit provided on a rotary portion so as to be opposed to thesuperconductor unit, the rotary portion being contactlessly supportedrelative to the fixed portion by the pinning effect of a superconductorconstituting the superconductor unit, the superconductive magneticbearing being characterized in that the permanent magnet unit comprisesa plurality of permanent magnet members arranged in superposed layerswith an insulating layer provided between each adjacent pair of magnetmembers.
 2. A superconductive magnetic bearing according to claim 1which is characterized in that the superconductor unit comprises aplurality of circumferentially divided superconductor bulks.
 3. Asuperconductive magnetic bearing according to claim 1 or 2 which ischaracterized in that the rotatable bearing portion comprises theannular permanent magnet unit and an annular yoke adjacent to thepermanent magnet unit and opposed to the superconductor unit, the yokecomprising a plurality of yoke members made of a magnetic material andarranged in superposed layers with an insulating layer interposedbetween each adjacent pair of yoke members.